The reasons for the aging of high-voltage pulse capacitors
Sep 17, 2025| High-voltage pulse capacitors are key components in power electronic systems and are widely used in laser generators, pulse power sources, electromagnetic forming, medical equipment, and particle accelerators, among others. Their working characteristic is to withstand extremely high voltage and current rate changes within a very short period of time. However, like other capacitors, they will inevitably experience performance degradation, or aging, during long-term operation.
Ⅰ. Electrical stress aging: The most direct factor
⑴ Partial discharge: This is the primary cause of aging in high-voltage capacitors.
Mechanism: When there are bubbles, impurities inside the capacitor dielectric, or if the electric field intensity at the electrode edges is overly concentrated, the electric field strength in these areas will exceed the local breakdown field strength of the medium. As a result, small, repetitive breakdowns and extinguishments occur, which is known as local discharge.
⑵ Overvoltage:
Overvoltage: Even a brief overvoltage operation may exceed the tolerance limit of the medium, directly causing insulation damage and significantly accelerating the aging process.
II. Thermal Stress Aging: The Chronic Killer of Performance
⑴ Dielectric loss heating: Capacitors generate heat due to dielectric loss under an alternating electric field. In high-voltage pulse applications, the voltage (U) is extremely high, and although the frequency (f) is not high, the amount of heat generated is still considerable.
⑵ ESR loss and heat generation: The equivalent series resistance (ESR) of the capacitor generates joule heat when passing through a large pulse current (Ipulse). This is the primary source of heat generation for pulse capacitors.
⑶ Thermal accumulation effect: If the generated heat is greater than the dissipated heat, the temperature inside the capacitor will continue to rise. High temperature will: reduce the insulation strength of the dielectric. Accelerate the chemical degradation reactions within the dielectric.
III. Chemical and Physical Aging of Dielectric Materials
⑴ Degradation of dielectric materials: Commonly used polymer materials such as polypropylene film (BOPP) may experience molecular chain breakage, cross-linking or oxidation under long-term electric field exposure, resulting in a gradual deterioration of dielectric properties.
⑵ Aging of the impregnating agent: The function of the impregnating agent is to fill the gaps between the films, enhance the pressure resistance and improve heat dissipation. However, the impregnating agent will gradually oxidize, polymerize or absorb moisture, resulting in a decrease in its dielectric constant and insulation performance, and losing its protective effect.
⑶ Electrochemical Corrosion: The intrusion of moisture and oxygen is the enemy of capacitors. They will undergo electrochemical reactions with the electrodes of the metallized film (usually the zinc-aluminum layer), resulting in electrode corrosion and evaporation, manifested as a steady decline in capacitance (C) and an increase in equivalent series resistance (ESR). This is the main aging mode when the "self-healing" ability of the metallized film capacitor is exhausted.